Microanalysis of Single Poly(N-isopropylacrylamide) Droplet Produced by an Optical Tweezer in Water: Isotacticity Dependence of Growth and Chemical Structure of the Droplet
Microanalysis of Single Poly(N-isopropylacrylamide) Droplet Produced by an Optical Tweezer in Water: Isotacticity Dependence of Growth and Chemical Structure of the Droplet
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光镊在水中产生的单个聚（N-异丙基丙烯酰胺）液滴的微量分析：液滴生长和化学结构的全同立构规整度依赖性
DOI：
10.1021/acs.jpcb.0c06932
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Tsuboi Yasuyuki
中科院分区：
文献类型：
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作者：
Ushiro Kenta;Shoji Tatsuya;Matsumoto Mitsuhiro;Asoh Taka-Aki;Horibe Hideo;Katsumoto Yukiteru;Tsuboi Yasuyuki
采用光镊-拉曼显微光谱技术研究了聚N-异丙基丙烯酰胺（PNIPAM）水溶液的温敏相分离机理。将近红外激光束（λ = 1064 nm）聚焦到溶液中以在光学显微镜下产生并捕获单个聚合物微滴。激光束起着两个重要的作用：第一个作用是局部加热溶液以诱导相分离，其中在焦点周围产生许多聚合物微滴，而第二个作用是收集这些微滴。最终，稳定地产生单个聚合物液滴并将其捕获在焦点处。我们的方法使我们能够对液滴进行两种类型的微量分析。分析I是实时监测聚合物液滴的生长，通过其我们可以确定液滴的生长速率。分析II是揭示液滴的化学成分的拉曼显微光谱。通过这两个分析，我们揭示了重要的相分离机制的立构规整性（全同立构规整度）的依赖。从分析I，我们表明，液滴的增长是由奥斯特瓦尔德熟化机制和增长加速，通过增加的全同立构规整度。从分析II，我们表明，凝胶化促进液滴（物理凝胶形成），增加全同立构规整度。我们的技术应该是一个多功能的工具，探索各种二元溶液体系的液-液相分离机制。
Thermoresponsive phase separation mechanisms of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions were investigated using an optical tweezer combined with a Raman microspectroscope. A near-infrared laser beam (λ = 1064 nm) was focused into the solution to produce and trap a single polymer microdroplet under an optical microscope. The laser beam played two important roles: The first role is to locally heat the solution to induce phase separation in which numerous polymer microdroplets are generated around the focus, while the second one is to collect these microdroplets. Eventually, a single polymer droplet was stably produced and trapped at the focus. Our method enabled us to perform two types of microanalysis for the droplet. Analysis I is real-time monitoring the growth of the polymer droplets by which we can determine the growth rate of droplets. Analysis II is Raman microspectroscopy to reveal chemical components of the droplets. By means of these two analyses, we revealed important phase separation mechanisms in terms of stereoregularity (isotacticity) dependence. From analysis I, we show that droplet growth is governed by the Ostwald ripening mechanism and the growth is accelerated by increasing the isotacticity. From analysis II, we show that the gelation is promoted in the droplet (physical gel formation) with increasing isotacticity. Our technique should be a versatile tool to explore liquid–liquid phase separation mechanisms for various binary solution systems.